Convergence magnet pole shoes



Nov. 21, 1967 R. F. DE BOTH CONVERGENCE MAGNET POLE SHOES Filed Feb. 28,1966 INVENTOR, Raymond F De Both 2 BY Arrorney United States PatentOfifice 3,354,337 C(JNVERGENCE MAGNET PDLE SHQES Raymond F. De Both,Broadview, Ill., assignor to Zenith Radio Corporation, Chicago, L, acorporation of Delaware Filed Feb. 28, 1966, Ser. No. 530,268 8 Claims.((31. 313--'77) The subject invention relates, in general, to colortelevision but more particularly to electromagnetic convergenceapparatus for use with tri-beam color reproducing cathode ray tubes.

A cathode ray tube of the type employed in conventional color televisionreceivers comprises a delta array of electron guns which generate anddirect a trio of electron beams towards the target structure of thetube. The target includes a luminescent screen comprising an or deredgrouping of red, green and blue phosphor dots. These phosphor dots arearranged in a plurality of primary color triads, i.e., each triad isformed of a red, a green and a blue phosphor dot. Disposed adjacent thescreen is a mask having a like plurality of apertures, one inregistration with each color triad.

During scansion, the three beams must substantially converge at or nearthe plane of the aperture mask if proper color reproduction is to beachieved. When properly converged the three beams instantaneouslyilluminate only the phosphor dots included within a particular triad.

The geometry of a shadow-mask tube, however, is such that the threebeams do not naturally converge at all points of the raster duringscansion. Normally, static as well as dynamic convergence is required.To achieve such convergence it is known to subject the beams toauxiliary magnetic fields. Static convergence is conventionallyaccomplished by the use of permanent magnets which are adjustablysupported about the neck of the tube. These magnets direct their fluxtoward magnetic circuits disposed within the neck section of the tube.One such circuit is provided for each beam and typically takes the formof a pair of elongated pole pieces which flank the path of its assignedelectron beam and thereby direct the field of the magnet across the pathof the beam.

Dynamic convergence is attained by resort to electromagnetic apparatuswhich also directs magnetic flux into the internal pole pieces. Theseelectromagnets are energized by correction signals derived from thehorizontal and vertical deflection circuits. The electromagneticapparatus, as well as the permanent magnets are commonly mounted on ayoke which is adjustably positionable about the neck of the tube.

A typical prior art electromagnetic convergence device comprises aU-shaped core having a vertical and a horizontal convergence Windingmounted in tandem on each leg of the core. The total flux realizablefrom such an electromagnetic core is determined by the core material,its dimensions, the windings and the input energy. The magnitude of fluxtransferable from such a core to an adjoining magnetic circuit, on theother hand, is determined principally by the reluctance encountered bythe flux. This, in turn, is a function of the proximity of the magneticcircuits and their configurations.

In a cathode ray tube the proximity of the electromagnetic device to theinternal pole pieces is established, of course, by the wall thickness ofthe tube neck and the housing which supports the device. Theconfiguration of the internal magnetic circuit is dictated by electrongun considerations while the shape of the electromagnet core has beendetermined by space and economy factors. Space is conserved and somecore and coil material economies are eifected if the electromagneticdevice is physically reduced in size. This expedient, however,undesirably in- 3,354,337 Patented Nov. 21, l fi? creases the reluctanceof the flux coupling path between the core and the internal pole piecesthereby taxing the correction signal source and, as a consequence,reducing the efficiency of the convergence system.

It is therefore a general object of the invention to provide an improvedconvergence apparatus for use with multi-beam color reproducing cathoderay tubes.

It is a specific object of the invention to provide a more efficientelectromagnetic device for use in dynamic convergence apparatus.

It is also an object of the invention to obtain a more eflicientconvergence apparatus in an economical fashion.

In accordance with the invention an electromagnetic device for use withconvergence apparatus employed with a multi-beam cathode ray tube havinga pole piece pair associated with at least one of the beams andcomprising outwardly directed pole faces, comprises a core of magneticmaterial having a pair of spaced apart legs. A convergence winding issupported upon the core. Additionally, the device comprises a pair offlux permeable pole shoes having respective areas greater than the areaof a core leg extremity. Means are included for supporting the poleshoes adjacent the extremities of the core legs and mounting means areprovided for mounting the core and the pole shoes upon the neck of thecathode ray tube with the pole shoes confronting the pole piece faces.

The features of this invention which are believed to be novel are setforth with particularity in the appended claims. The invention, togetherwith further objects and advantages thereof, may best be understood,however, by reference to the following description taken in conjunctionwith the accompanying drawings, in the several figures of which likereference numerals identify like elements, and in which:

FIGURE 1 is an elevational view, partly in section, of the inventiveconvergence apparatus positioned about the neck of a tri-beam cathoderay tube;

FIGURE 2 is an exploded view, partly in section, of a portion of theconvergence apparatus shown in FIG- URE 1;

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 1;

FIGURE 3a is a schematic representation of the magnectic fielddistribution across that portion of the convergence apparatus shown inFIGURE 3;

FIGURE 3b is a schematic representation of the magnetic fielddistribution in a prior art convergence apparatus; and

FIGURE 4 is a schematic diagram depicting the electrical circuitry ofthe conver ence coils shown in FIG- URES 1 and 2.

A convergence apparatus It? embodying the invention is depicted inFIGURE 1. As there shown, the conincident with the geometric axis of thetube itself. A trio of electron guns (not shown) is symmetricallydisposed above this axis and develops the electron beams 12, 112' and12". Supported within the neck portion of the tube and extendingradially from the tube axis are pairs of elongated metallic pole pieces13, 13' and 13''. These pole pieces, which are spaced about the tubeaxis on centers, present outer faces 14, 14, 14" to electromagneticdevices which are housed within convergence apparatus 10 and which willbe more fully described below. The inner extremities 15, 15, 15" ofthese pole pieces, on the other hand, confront the paths of respectiveelectron beams 12, 12' and 12" for substantially the entire lengths ofthe pole pieces. A Y-shaped magnetic shield 16 is interposed between theinternal pole pieces to prevent interaction of the magnetic fielddeveloped across them.

It is appreciated, of course, that a delta gun array is not employed inall multi-beam color reproducing cathode ray tubes. One alternativeconstruction, for example, contemplates an in-line or planar gun array.In such a construction a pole piece pair for the centrally disposed beammay be unnecessary.

Convergence apparatus In is of an interlocking tripartite constructioncomprising three substantially identical equally spaced units or lobes17, 17', 17". As best seen in FIGURE 1, each of the lobes includes anarmate wall section having a curvature conforming to the wall of tubeneck 11. A U-shaped spring 18 secures convergence apparatus at a desiredlocation upon neck 11, that is, with each of lobes 17, 17, 17 positionedover an assigned one of pole pairs 13, 13, 13", respectively.

Individually associated with each of lobes 17, 17 17 are staticconvergence magnets 19 (only two shown) which are mounted in holders 20adjustably supported upon outside walls of the lobes. With thisarrangement the flux fields of magnets 19 are presented to the outerfaces 14, 14', 14" of the internal pole pieces.

Each of lobes 17, 17', 17" houses identical structure for dynamicallyconverging its assigned beam; therefore, discussion will be confined toa consideration of lobe 17, the internal structure of which is detailedfor this purpose. Accordingly, and as is apparent from a considerationof FIGURES 1-3, lobe 17 is formed of a pair of matching half-shellswhich enclose an electromagnetic convergence device 22. Each half-shellcomprises pedestals 23 and a pair of pockets 24, which are formed in thearcuate wall section 25 of the shell, for supporting and positioningdevice 22.

Convergence device 22 comprises a U-shaped core 26 of magnetic materialhaving a pair of spaced apart legs 27. Core 26 is preferably constitutedof a high permeability material such as ferrite although other highpermeability materials are also suitable. The free extremities 28 oflegs 27 are inserted in wall pockets 24- and centrally positioned withinlobe 17 by virture of the support afiorded by pedestals 23. Extremities23 of the core legs are canted to accommodate the curvature of tube neck11 and, as apparent in FIGURE 2, have crosssectional areas substantiallysmaller than the areas of ad jacent pole faces 14.

Device 22 further comprises a pair of permeable pole shoes 29 havingrespective areas approximately the same as the areas of pole faces 14.More particularly, pole shoes 29 comprise strips of magnetic materialwhich are supported in an abutting relation with core leg extremities 28and in a parallel spaced relation to pole faces 14 by wall pockets 24,see FIGURE 3. Thus supported pole shoes 29 overlap core leg extremities28 in tWo directions, in fact, it is preferred that the pole shoes begeometrically centered with respect to the core legs. In this fashion,and as schematically illustrated in FIGURE 3a, a uniform non-magneticair gap is established between the external magnetic circuit, i.e., thepole shoes 29 of de vice 22, and faces 14 of pole piece 13. Preferably,pole shoes 29 are formed of thin rectangular strips of transformerlamination stock which is grain oriented in the direction of the longestdimension of the strip, that is, along its length.

A horizontal convergence winding 31 and a vertical convergence winding32 are mounted in a tandem arrangement on each of core legs 27. Asschematically shown in FIGURE 4, the end turns of each horizontalconvergence winding 31 are serially connected in a fluxaiding relation.In like fashion, the end turns of each verticalconvergence winding areserially. connected in a flux-aiding relation. The free ends of windings31 and 32 are returned, respectively, to horizontal and verticaldeflection circuits, not shown, for energization.

In operation, convergence apparatus 10 is mounted upon the neck of thepicture tube and positioned so that electromagnets 22 and magnets 19 arein juxtaposition with assigned ones of internal pole pieces 13, 13, 13".As already indicated, each of the electron beams passes between theconfronting inner extremities of an assigned pair of pole pieces. Themagnetic field extending across the ends of each pair of pole pieces issubstantially perpendicular to the trajectory of the beam thus producinga lateral deflection of the beam which is proportional to the strengthof the impressed field. By controlling the strength of these magneticfields, beam trajectories are altered so that the beams converge at agiven point on the tube screen.

In the absence of a control signal to the dynamic convergence windings31', 32, the flux passing through the internal pole pieces is determinedby magnets 19. The strength of these fields is determined by theorientation and the proximity of the magnet to the outer faces 14, 14',14" of the internal pole pieces, Accordingly, to achieve staticconvergence of the three beams, magnets 19 are adjusted until thedesired degree of convergence is attained.

Dynamic convergence of the electron beams, on the other hand, isaccomplished by electromagnets 22. More particularly, horizontal andvertical convergence Windings 31, 32 are energized by control signalsderived from the deflection system, which signals vary as functions ofthe horizontal and vertical scanning signals, respectively. Thesecontrol signals develop time-varying magnetic flux fields within core26. Again, confining attention specifically to the apparatus associatedwith lobe 17, the magnetic field developed in core 26 is directed viapole shoes 29 into the outer faces 14 of pole pieces 13. Asschematically depicted in FIGURE 3a, the magnetic flux generated bydevice 22 is uniformly distributed across the air gap between pole shoe29 and outer face 14 of the internal pole piece. As a result of suchdistribution, the reluctance of this air gap is reduced over that whichwould be presented to the core in the absence of the pole shoes. Thisobtains because the reluctance of the air gap is inversely proportionalto the confronting areas of the internal pole pieces and the externalmagnetic structure which, in this instance, constitutes pole shoes 29.

In the absence of a pole shoe Z9, and as illustrated in FIGURE 3b, anon-uniform flux field is developed between the extremity of a core leg28' and the face 14 of the internal pole piece. These magneticstructures, that is,

core leg 28 and pole face 14, present a higher reluctance to themagnetic field, for the reason above given, and, as a result, adverselyaffect the sensitivity of the dynamic convergence circuits. In otherwords, to achieve identical displacements of an electron beam, themagnetic structure of FIGURE 3b requires a greater driving power thanthe structure of FIGURE 3a.

Moreover, by employing strips of permeable material having a grainstructure oriented in the direction of the longest dimension for shoes29', the reluctance to the magnetic flux of device 22 is further reducedsince the grain structure of such a shoe more expeditiously distributesthe flux along the length of the shoe and therefore across the entirelength of air gap between the shoe and outer pole face 14. This uniformflux distribution is further enhanced by abutting the pole shoe againstthe extremity of the core leg and by centering the shoe relative to thecore leg.

Merely by way of illustration and in no sense by way of limitation, poleshoes constructed of transformer lamination stock M6X AAS and grainoriented in the longest dimension of the shoe have been successfullyemployed in an operative embodiment of the convergence apparatus shownin FIGURES 1-3. M6X is an American Iron and SteelInstitute-specificationfor a particular type of'grainoriented steel. The designation AAS standsfor Annealed After Stamping and simply means that the steel is annealedafter a forming or stamping operation in order to counter any stressesin the material due to such operation.

While the pole shoes are disclosed as substantially rectangular in crosssection this construction is not imperative but was employed in theoperative embodiment since it is a feasible configuration formagnetically cooperating with the internal pole pieces. It is moreimportant that the area and configuration of the pole shoe be such as toconfront substantially the entire face of the internal pole piece.

Insofar as multi-beam cathode ray tubes having gun arrays other than adelta configuration are concerned, it is recognized that such tubes mayrequire different convergence apparatus arrangements. For example,apparatus having two rather than three convergence units may beindicated and even a different type convergence winding may be moresuitable for a particular type tube. In any event, the disclosedmagnetic core and pole shoe arrangement finds particular utility inconvergence apparatus for use with any multi-beam cathode ray tubehaving one or more pairs of internal beam displacing pole pieces.

In summary, the objectives of the invention are achieved for multi-beamtubes of the type herein considered by virtue of the fact that thedisclosed electromagnet construction permits a magnetic convergencefield to be developed uniformly across the entire gap extending betweenthe external magnetic circuit and the internal pole pieces therebysignificantly increasing the sensitivity of the convergence system.

While a particular embodiment of the present invention has been shownand described, it is apparent that changes and modifications may be madetherein without departing from the invention in its broader aspects. Theaim of the appended claims, therefore, is to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

I claim:

1. In a convergence apparatus for use with a multibeam cothode ray tubehaving a pole piece pair associated with at least one of the electronbeams and comprising outwardly directed pole faces, an electromagneticdevice for selectively positioning one of said beams comprising:

a core or" magnetic material having a pair of spaced apart legs andsupporting a convergence winding;

a pair of permeable pole shoes having respective areas greater than thearea of a core leg extremity; means for supporting said pole shoesadjacent the extremities of said core legs;

and means for mounting said core and said pole shoes upon the neck ofsaid cathode ray tube with said pole shoes confronting said pole piecefaces.

2. An electromagnetic beam positioning device of the type defined inclaim 1, in which said pole shoes are supported in an abutting relationto the extremities of said core legs.

3. An electromagnetic beam positioning device of the type defined inclaim 1, in which said pole shoes are mounted in parallel spacedrelation to said pole faces.

4. An electromagnetic beam positioning device of the type defined inclaim 1, in which said pole shoes comprise thin planar rectangularstrips of magnetic material.

5. An electromagnetic beam positioning device of the type defined inclaim 4, in which said pole strips overlap said core leg extremities inat least two directions.

a. An electromagnetic beam positioning device of the type defined inclaim 4, in which said pole strips are supported geometrically centeredrelative to said core leg extremities.

7. An electromagnetic beam positioning device of the type defined inclaim 4, in which said pole shoe material is grain oriented parallel tothe longest dimension of said strip.

8. An electromagnetic beam positioning device of the type defined inclaim in which the respective areas of said pole shoes approximate theareas of said pole faces.

References Cited UNITED STATES PATENTS 1/1949 Bradley 313-77 6/1964Heuer et al 3l377

1. IN A CONVERGENCE APPARATUS FOR USE WITH A MULTIBEAM COTHODE RAY TUBEHAVING A POLE PIECE PAIR ASSOCIATED WITH AT LEAST ONE OF THE ELECTRONBEAMS AND COMPRISING OUTWARDLY DIRECTED POLE FACES, AN ELECTROMAGNETICDEVICE FOR SELECTIVELY POSITIONING ONE OF SAID BEAMS COMPRISING: A COREOF MAGNETIC MATERIAL HAVING A PAIR OF SPACED APART LEGS AND SUPPORTING ACONVERGENCE WINDING; A PAIR OF PERMEABLE POLE SHOES HAVING RESPECTIVEAREAS GREATER THAN THE AREA OF A CORE LEG EXTREMITY; MEANS FORSUPPORTING SAID POLE SHOES ADJACENT THE EXTREMITIES OF SAID CORE LEGS;AND MEANS FOR MOUNTING SAID CORE AND SAID POLE SHOES UPON THE NECK OFSAID CATHODE RAY TUBE WITH SAID POLE SHOES CONFRONTING SAID POLE PIECEFACES.